Screening Methods for Antifertility Agents

Introduction & scope

• Definition — Antifertility agents prevent fertility by interfering with one or more steps of the normal reproductive cycle in either sex; screening methods are the validated bench-to-animal assays used to detect and quantify that interference before clinical contraceptive development.
• Unit of study — This is an experimental-pharmacology / drug-screening topic — the unit examined is the validated model + endpoint + reference (standard) drug, not clinical contraceptive pharmacotherapy.
• Two organising axes — (a) Target sex — female vs male methods; (b) hormonal mechanism class screened — estrogenic / anti-estrogenic, progestational / anti-progestational, androgenic / anti-androgenic — plus the integrated fertility endpoints (anti-ovulatory, anti-implantation, abortifacient, anti-spermatogenic/spermicidal).
• Female targets — five interception points — Inhibition of ovulation; prevention of fertilization; interference with ovum transport; interference with implantation; destruction of the early implanted embryo (abortifacient / contragestational).
• Male target & design constraint — Interference with spermatogenesis or sperm function, without loss of libido or secondary sexual characteristics — the central design constraint of male antifertility screening.
• Quantification — Each assay is reported against a standard (reference) drug, so test-compound potency is expressed as an ED₅₀ ratio or % response relative to that standard.